Rescan cells at the end of mark-sweep. This means they don't need a

write barrier.
Review URL: http://codereview.chromium.org/8816021

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@10187 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/ia32/code-stubs-ia32.cc

@@ -4657,7 +4657,8 @@ void CallFunctionStub::Generate(MacroAssembler* masm) {
     // megamorphic.
     __ cmp(ecx, Immediate(UninitializedSentinel(isolate)));
     __ j(equal, &initialize, Label::kNear);
-    // MegamorphicSentinel is a root so no write-barrier is needed.
+    // MegamorphicSentinel is an immortal immovable object (undefined) so no
+    // write-barrier is needed.
     __ mov(FieldOperand(ebx, JSGlobalPropertyCell::kValueOffset),
            Immediate(MegamorphicSentinel(isolate)));
     __ jmp(&call, Label::kNear);
@@ -4665,14 +4666,7 @@ void CallFunctionStub::Generate(MacroAssembler* masm) {
     // An uninitialized cache is patched with the function.
     __ bind(&initialize);
     __ mov(FieldOperand(ebx, JSGlobalPropertyCell::kValueOffset), edi);
-    __ mov(ecx, edi);
-    __ RecordWriteField(ebx,
-                        JSGlobalPropertyCell::kValueOffset,
-                        ecx,
-                        edx,
-                        kDontSaveFPRegs,
-                        OMIT_REMEMBERED_SET,  // Cells are rescanned.
-                        OMIT_SMI_CHECK);
+    // No need for a write barrier here - cells are rescanned.
 
     __ bind(&call);
   }
@@ -4704,6 +4698,8 @@ void CallFunctionStub::Generate(MacroAssembler* masm) {
     // non-function case.
     __ mov(ebx, Operand(esp, 0));
     __ mov(ebx, Operand(ebx, 1));
+    // MegamorphicSentinel is an immortal immovable object (undefined) so no
+    // write barrier is needed.
     __ mov(FieldOperand(ebx, JSGlobalPropertyCell::kValueOffset),
            Immediate(MegamorphicSentinel(isolate)));
   }

src/ia32/lithium-codegen-ia32.cc

@@ -2144,20 +2144,7 @@ void LCodeGen::DoStoreGlobalCell(LStoreGlobalCell* instr) {
 
   // Store the value.
   __ mov(FieldOperand(object, offset), value);
-
-  // Cells are always in the remembered set.
-  if (instr->hydrogen()->NeedsWriteBarrier()) {
-    HType type = instr->hydrogen()->value()->type();
-    SmiCheck check_needed =
-        type.IsHeapObject() ? OMIT_SMI_CHECK : INLINE_SMI_CHECK;
-    __ RecordWriteField(object,
-                        offset,
-                        value,
-                        address,
-                        kSaveFPRegs,
-                        OMIT_REMEMBERED_SET,
-                        check_needed);
-  }
+  // Cells are always rescanned, so no write barrier here.
 }
 
 

src/ia32/stub-cache-ia32.cc

@@ -2522,23 +2522,9 @@ Handle<Code> StoreStubCompiler::CompileStoreGlobal(
 
   // Store the value in the cell.
   __ mov(cell_operand, eax);
-  Label done;
-  __ test(eax, Immediate(kSmiTagMask));
-  __ j(zero, &done);
-
-  __ mov(ecx, eax);
-  __ lea(edx, cell_operand);
-  // Cells are always in the remembered set.
-  __ RecordWrite(ebx,  // Object.
-                 edx,  // Address.
-                 ecx,  // Value.
-                 kDontSaveFPRegs,
-                 OMIT_REMEMBERED_SET,
-                 OMIT_SMI_CHECK);
+  // No write barrier here, because cells are always rescanned.
 
   // Return the value (register eax).
-  __ bind(&done);
-
   Counters* counters = isolate()->counters();
   __ IncrementCounter(counters->named_store_global_inline(), 1);
   __ ret(0);

src/mark-compact.cc

@@ -2081,6 +2081,24 @@ void MarkCompactCollector::MarkLiveObjects() {
 
   PrepareForCodeFlushing();
 
+  if (was_marked_incrementally_) {
+    // There is no write barrier on cells so we have to scan them now at the end
+    // of the incremental marking.
+    {
+      HeapObjectIterator cell_iterator(heap()->cell_space());
+      HeapObject* cell;
+      while ((cell = cell_iterator.Next()) != NULL) {
+        ASSERT(cell->IsJSGlobalPropertyCell());
+        if (IsMarked(cell)) {
+          int offset = JSGlobalPropertyCell::kValueOffset;
+          StaticMarkingVisitor::VisitPointer(
+              heap(),
+              reinterpret_cast<Object**>(cell->address() + offset));
+        }
+      }
+    }
+  }
+
   RootMarkingVisitor root_visitor(heap());
   MarkRoots(&root_visitor);